Conventionally, road vehicles have operated with fuel, usually a hydrocarbon fuel such as gasoline, road diesel fuel, or even compressed natural gas, stored onboard the vehicle with the supply replenished at intervals as the fuel is consumed. Typically, liquid fuel such as gasoline and diesel fuel are replenished from dispensing units commonly referred to as fuel pumps at roadside service stations. Other consumables used in the vehicle, such as engine oil, transmission fluid and other fluids, are generally replaced only when the vehicle is serviced at extended intervals, generally at intervals of a few thousand miles. Thus, the only consumable material requiring frequent replenishment has been the fuel.
Current concerns about the environmental effects of the internal combustion engine have led to regulations on vehicle emissions, both evaporative and combustive, and significant efforts have been made in the vehicle industry as well as the fuel industry to reduce levels of emission, especially of pollutants such as sulfur oxides (SO.sub.x), nitrogen oxides (NO.sub.x) and carbon monoxide (CO). Significant improvements have been achieved by the use of catalytic converters onboard vehicles but further improvements are desired, particularly with respect to nitrogen oxide emissions. Unlike emissions of sulfur oxides which are dependent upon the amount of sulfur in the fuel, a factor which is capable of control by suitable refining technology, nitrogen oxides tend to be produced primarily by a combination of atmospheric nitrogen and oxygen under the conditions encountered in the combustion chamber of an internal combustion engine.
Nitrogen oxides may be reduced to nitrogen by reaction with ammonia under selective catalytic reduction (SCR) conditions, but as ammonia would present hazards in the event of an accident to a vehicle containing it, it is unattractive for use in conventional road vehicles. One alternative, however, is the use of urea as a source of ammonia because urea can undergo thermal decomposition and hydrolysis to form ammonia, which then reacts with nitrogen oxides under SCR conditions in a suitable catalytic converter. Although urea is a solid, it can be used in the form of an aqueous solution, which is convenient for storage on the vehicle during use and for dispensing into the vehicle. An aqueous urea solution can also be injected into the engine/exhaust system to undergo thermal decomposition and hydrolysis to form ammonia, which can then react with nitrogen oxides as desired. Provided that the aqueous system can be prevented from solidifying by addition of suitable additives, aqueous urea solutions represent a desirable solution to the problem of controlling emissions of nitrogen oxides.
Of particular importance for aqueous urea solutions is the prevention of solidification at the low temperatures usually encountered by vehicle users in the colder climatic regions. Freezing is a particular problem of aqueous-based solutions thus creating a need for liquid exhaust treatments that will maintain the liquid state down to storage temperatures of at least about -20.degree. F. (about -30.degree. C.). In consideration of the potential application of SCR methods for the lowering of nitrogen oxide emissions in motor vehicle exhaust, specific urea formulations that will resist freezing at low temperatures are especially desirable.
Constraining design factors pertaining to fuel additive dispensing systems include that the additive dispensing and emission control systems be robust, easy to use and maintain by skilled and unskilled persons, and be inexpensive in view of the large number of road vehicles currently in use and the social need for improved vehicle technology to be readily accessible to all members of the community. Therefore, the vehicle may be equipped with a self-contained system that provides the vehicle with sufficient fuel additive (treatment agent) such that replenishment is necessary only at extended intervals coinciding with the regular service intervals of the vehicle. However, with service intervals, whether for oil changes or mechanical attention, becoming necessary only at increasingly extended intervals, it is possible that the supply of fuel additive could become depleted between regular servicing intervals, particularly if the need for regular servicing is neglected, as it often is. Alternatively, the vehicle may be equipped with a system that replenishes the supply of fuel additive or treatment agent whenever the fuel is replenished, thereby ensuring that the supply of treatment agent or fuel additive is available as long as fuel is available. From the point of view of ensuring constant supply of the fuel additive or treatment agent, this approach is preferred.
Dual tank systems generally have been described in U.S. Pat. Nos. 3,884,255 and 4,852,892. These systems, however, possess dual tanks that are designed to hold identical liquids and are either filled separately or simultaneously by means of a cross-over connection between tanks. Similarly, the systems described in U.S. Pat. Nos. 4,161,160 ('160 patent), 4,596,277 ('277 patent), and 5,331,994 ('994 patent) contain a fuel additive tank and at least one fuel tank. The systems disclosed in the '160, '277 and '994 patents, however, are not designed to feed fuel additive and fuel individually, but simultaneously, during replenishment. For example, the '160 patent discloses a diesel fuel supply system in which the fuel additive is added to the fuel tank. Similarly, the '994 patent is directed to an additive dispensing system in which metered quantities of fuel additive are added to fuel in a fuel tank. Furthermore, the '277 patent discloses a metering system for adding a fuel additive to fuel in the fuel tank of an internal combustion engine.
From the point of view of convenience to the vehicle operator, it is desirable that the treatment agent or fuel additive be added at the same time as the fuel, without any additional effort or manipulation on the part of the operator, and further to ensure that replenishment of the treatment agent takes place substantially concurrently with the fueling process. The present invention is directed to an integrated dispensing system which meets these requirements.